riffraff:Depending on the size of the engine, a starter-generator on the engine hooked to a set of batteries or a starter-generator on the APU

Most of the turbo-fan engines on passenger jets are NOT started electrically. They are started pneumatically. I believe 787 is the exception, though I'm not sure about A380.

You have an "Air Turbine Starter" which is about the size of a 4-slice toaster or as large as toaster-oven. It has a turbine blade on one end that will spin up to about 60-70KRPM. That small turbine wheel, which is about 3-6" in diameter connects to a set of gears which have a ridiculous gear ratio and connect to an output shaft. The output shaft will spin up to about 5K rpm and is connected to the gearbox of the engine, thus getting the engine started.

The ones that are about the size of a toaster-oven, which are used on 777/A330 put out about 400hp.

kidgenius:riffraff: Depending on the size of the engine, a starter-generator on the engine hooked to a set of batteries or a starter-generator on the APU

Most of the turbo-fan engines on passenger jets are NOT started electrically. They are started pneumatically. I believe 787 is the exception, though I'm not sure about A380.

You have an "Air Turbine Starter" which is about the size of a 4-slice toaster or as large as toaster-oven. It has a turbine blade on one end that will spin up to about 60-70KRPM. That small turbine wheel, which is about 3-6" in diameter connects to a set of gears which have a ridiculous gear ratio and connect to an output shaft. The output shaft will spin up to about 5K rpm and is connected to the gearbox of the engine, thus getting the engine started.

The ones that are about the size of a toaster-oven, which are used on 777/A330 put out about 400hp.

How exactly is 12:1 to 14:1 a "ridiculous gear ratio"?

I'll start passing the word at work, since we can build up to 119:1 in a single reduction stage. We have apparently gone beyond plaid.

While TFA is interesting, they fail to point out the whole thing that makes it interesting. Turbines are wonderfully efficient engines, but they suffer from requiring very high compression to operate. For example, one turbine I'm familiar with can only operate (unassisted) once it reaches 50% of it's maximum speed. An APU has to spin it up to about 20% of it's max speed, and then it uses igniters to get it up to 50%. Only once it spins fast enough does it have the necessary compression to be self-sustaining.

For analogy, it'd be like if your car would only operate between 2000-4000 RPM, and you needed a second special motor to get the primary motor up to 2000RPM.

Too bad they don't have a video or something like that. The sound of a turbine engine starting is incredible. I can't access youtube right now but there is a video of a Bell helicopter starting and it is sweet. You hear the starter spinning up and the clicking of the igniters, then a roar as the fuel is added and begins combusting. Then the whine of the turbine rising in pitch as it spins faster and faster.

Tobin_Lam:You hear the starter spinning up and the clicking of the igniters, then a roar as the fuel is added and begins combusting. Then the whine of the turbine rising in pitch as it spins faster and faster.

kidgenius:riffraff: Depending on the size of the engine, a starter-generator on the engine hooked to a set of batteries or a starter-generator on the APU

Most of the turbo-fan engines on passenger jets are NOT started electrically. They are started pneumatically. I believe 787 is the exception, though I'm not sure about A380.

You have an "Air Turbine Starter" which is about the size of a 4-slice toaster or as large as toaster-oven. It has a turbine blade on one end that will spin up to about 60-70KRPM. That small turbine wheel, which is about 3-6" in diameter connects to a set of gears which have a ridiculous gear ratio and connect to an output shaft. The output shaft will spin up to about 5K rpm and is connected to the gearbox of the engine, thus getting the engine started.

The ones that are about the size of a toaster-oven, which are used on 777/A330 put out about 400hp.

I guess it really depends on the airplane. I've seen the APU from C-130Js and they aren't small at all. They are more along the lines of large truck engine.

"The exhaust is from the auxiliary power unit," Brand says. "The APU is like a mini jet engine, usually located in the back of the plane, containing a compressor, combustor, and turbine, that provides the plane with electricity and compressed air for the air conditioning system while the plane is on the ground." The APU also provides the first step in starting the jet's main engines and causing its blades to rotate at the tens of thousands of RPMs necessary for the engine to become sufficiently self-sustaining and propel the plane through liftoff and flight.

Newer airports have GPU (Ground Power Units) that basically plug-in the plane to the building like an electric car, to further reduce emissions from parked aircraft, and consumes none/less of the aircrafts fuel.

They either connect from the ground, or are built in to the jetway.

Same with refueling. at an older gate, you have the truck come and connect to the aircraft like a car. At more advanced gates, the fuel system is underground, and you just need a hose to connect the two. Makes for less vehicle traffic on the apron.

LemSkroob:the fuel system is underground, and you just need a hose to connect the two. Makes for less vehicle traffic on the apron.

Its a tad more than just a hose. To utilize a center point fueling system on an aircraft from underground storage, you'll notice they use a relatively small cart which has a pump, and flow metering hardware, and a filtering system.

When our unit got rid of F-105's, they had a 24 jet fly-over. Only 10 Dash-60's to provide bleed air for starts, so they decided to "Cart-Start" all 24 of them, at once. BOOM! Big clouds of smoke billowing, and the satisfying whine and spool up of 24 Pratt-Whitney J-75's. Pilots were told, if you've got an engine, hydraulics, and radio, you're going. They all went.

markie_farkie:Tobin_Lam: You hear the starter spinning up and the clicking of the igniters, then a roar as the fuel is added and begins combusting. Then the whine of the turbine rising in pitch as it spins faster and faster.

Sliding Carp:markie_farkie: Tobin_Lam: You hear the starter spinning up and the clicking of the igniters, then a roar as the fuel is added and begins combusting. Then the whine of the turbine rising in pitch as it spins faster and faster.

Fubini:While TFA is interesting, they fail to point out the whole thing that makes it interesting. Turbines are wonderfully efficient engines, but they suffer from requiring very high compression to operate. For example, one turbine I'm familiar with can only operate (unassisted) once it reaches 50% of it's maximum speed. An APU has to spin it up to about 20% of it's max speed, and then it uses igniters to get it up to 50%. Only once it spins fast enough does it have the necessary compression to be self-sustaining.

For analogy, it'd be like if your car would only operate between 2000-4000 RPM, and you needed a second special motor to get the primary motor up to 2000RPM.

True, but the flipside of that is that you have access to something like 50% of your engine power in the top 3% of RPM. Unbelievably smooth operation compared to recips.

It's a shame the materials required for a reliable hot section are so expensive, turbine-electric hybrid cars would be awesome.